(1) Field of the Invention
The present invention relates to an aligning method for overlaying a plurality of second patterns to be formed with plural shots of exposure over first patterns formed with one shot of exposure on a substrate.
(2) Description of the Related Art
To form fine patterns of semiconductor devices, etc., in the exposure process, phase shift masks, such as halftone phase shift mask, Levenson phase shift mask, etc. are used. The exposure with phase shift masks improves the exposure latitude, focal depth, etc. and is effective to form fine patterns. However, the phase shift masks are expensive, and recently, the mask (reticle) cost increase is a large serious problem.
As a countermeasure to the mask const increase, it is proposed to use a multilayer reticle (hereinafter called “MLR”) having plural layers of patterns arranged in one sheet of reticle.
FIG. 19 is a plan view of an MLR having two layers of patterns arranged in one sheet of reticle. As illustrated, in one sheet of reticle 100, a shot region 102 having a pattern of, e.g., the first interconnection layer, and a shot region 104 having a pattern of e.g., the second interconnection layer are arranged.
The MLR has the merit of reducing the mask cost. However, on the other hand, the MLR has the demerit that the exposure region per one layer of a pattern is smaller and thus the throughput of the exposure tool is decreased. Due to this, it is considered to use the MLR limitedly for layers using expensive masks, such as the phase shift mask, the mask for critical layers, etc.
In the exposure process for the masks, usually, different mask processes, in which, for example, positive resists are used, or negative resists are used, are used for respective layers using reticles. Kinds of the masks, such as binary masks or phase shift masks, are also different. Accordingly, it is difficult to arrange patterns of layers using different mask processes and different kinds of masks in one sheet of reticle.
As described above, the MLR is used to limited layers. Accordingly, in the actual manufacturing steps, a reticle other than the MLR (hereinafter called “single-layer reticle (SLR)”) must be also used for the exposure. That is, in the actual manufacturing steps, the mix-and-match exposure of the exposure using the SLR (hereinafter called “SLR exposure”) and the exposure using the MLR (hereinafter called “MLR exposure”) must be made.
FIG. 20A is a plan view of a shot layout of the SLR exposure, and FIG. 20B is a plan view of a shot layout of the MLR exposure to be overlaid over the shots of the SLR exposure. In FIG. 20, over one shot 106 of the SLR exposure, two shots 108 of the MLR exposure must be overlaid.
However, the mix-and-match exposure of the conventional SLR exposure and the MLR exposure has often found it difficult to overlay plural shots of the MLR exposure over one shot of the SLR exposure with high accuracy.